Initial K3 snapshot: 0.5B KDA/MLA/MoE train path

Standalone tree split from LLMRL/projects/kda. Includes Triton dt_bias
backward fix, train_k3 --preset 0.5b, SFT, Docker runtime, and tests.

kda/training/success.py

@@ -0,0 +1,86 @@
+"""Frozen translation success() — SFT eval and RL reward must call this."""
+
+from __future__ import annotations
+
+import re
+
+CHRF_MIN = 40.0
+COPY_CHRF_MAX = 80.0
+_CJK = re.compile(r"[\u4e00-\u9fff]")
+
+
+def _detect_lang(text: str) -> str | None:
+    sample = text.strip()
+    if not sample:
+        return None
+    try:
+        from langdetect import detect
+
+        tag = detect(sample)
+    except Exception:
+        if _CJK.search(sample):
+            return "zh"
+        if any(c.isascii() and c.isalpha() for c in sample):
+            return "en"
+        return None
+    if tag.startswith("zh"):
+        return "zh"
+    return tag[:2]
+
+
+def _chrf(hyp: str, ref: str) -> float:
+    """chrF++ in 0–100. Falls back to char unigram F if sacrebleu is missing."""
+    if not hyp or not ref:
+        return 0.0
+    try:
+        from sacrebleu.metrics import CHRF
+
+        return float(CHRF(word_order=2).sentence_score(hyp, [ref]).score)
+    except Exception:
+        hyp_c, ref_c = list(hyp), list(ref)
+        if not hyp_c:
+            return 0.0
+        ref_set = set(ref_c)
+        overlap = sum(1 for c in hyp_c if c in ref_set)
+        prec = overlap / len(hyp_c)
+        rec = overlap / max(len(ref_c), 1)
+        if prec + rec == 0:
+            return 0.0
+        return 100.0 * 2 * prec * rec / (prec + rec)
+
+
+def translation_success(
+    src: str,
+    hyp: str,
+    ref: str | None = None,
+    *,
+    target_lang: str,
+    chrf_min: float = CHRF_MIN,
+    copy_chrf_max: float = COPY_CHRF_MAX,
+) -> bool:
+    """Binary task success for zh↔en instruction translation.
+
+    1. non-empty hyp, no instruction leak prefix
+    2. langid(hyp) matches target_lang (zh / en)
+    3. hyp is not a copy of src
+    4. if ref is given, chrF(hyp, ref) >= chrf_min
+    """
+    hyp = hyp.strip()
+    src = src.strip()
+    if not hyp:
+        return False
+    leak = ("翻译如下", "translate to", "translation:", "译文：")
+    head = hyp[:40].lower()
+    if any(p in head or p in hyp[:20] for p in leak):
+        return False
+    want = "zh" if target_lang.startswith("zh") else "en"
+    got = _detect_lang(hyp)
+    if got != want:
+        return False
+    if src and _chrf(hyp, src) >= copy_chrf_max:
+        return False
+    if hyp == src:
+        return False
+    if ref is not None and _chrf(hyp, ref.strip()) < chrf_min:
+        return False
+    return True